Coolant flows top to bottom.

We're back to "is thermostat installed correctly? Is thermostat opening at correct temp?"

Have you measured radiator temp with a thermometer to confirm temp? What caused you to change the thermostat to begin with?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

I suspect that the Walmart automotive department sells some stuff specifically designed for use in automobiles. And if Walmart doesn't have it, any auto parts store worth its salt will.

Remove the thermostat and do a test drive.

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85 300CD Gramps 390K
89 190D Baby 322K
93 300D Grumpy 176K
99 SLK230

Considering that the pump is new, that might not be all that probable.

On the subject of the pump, however, it is possible to get a pump (especially an overhauled pump) that has vanes oriented in the wrong direction. (That happens quite often with some domestic engines that have different drive belt configurations in different vehicles.) Incorrect belt routing can also cause a water pump to rotate backwards in some applications.

Only a few components to deal with :
Radiator
Thermostat
Water pump
Block

With a hot upper and cold lower, indicating zero flow, its looking like either
a bad thermostat or a bad water pump.

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

I replaced the thermostat because the radiator was cold. I'm sure it's in correctly and I would be surprised if the old one was bad as well as the new one. I would like to take it out completely for testing purposes but I don't think there is a way without it leaking. I suppose I could gut out an old one. It seems to me that the pump may be at fault. Im going to try to find a picture of a new one and compare vanes.

I'm thinking pump. Cavitation pitting can destroy the pump over years/miles of incorrect or inadequate coolant.

To test the thermostat, heat some water on the stove with the thermostat in it, observe the temperature where it opens with a thermometer.

IIRC the cooling system does not circulate correctly without the thermostat in the housing, I might be thinking of the wrong engine though.

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Gone to the dark side

- Jeff

If the title of the thread is any indication, that's not the problem.

I pulled the guts out of an old one, and stuck it in there with the oring in place to flush and clean everything.
do you still have the old pump?

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My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Just a quick update.

I tested the old thermostat in a pan on the stove. It pops open at around 85C, definitely not 80C. I don't think this would cause the type of overheating i'm seeing but I gut it anyway and install.

Around town the temp now hovers around 80 maybe a little more. When you stop the car the radiator is only moderately warm all over. Taking the car on the highway things change. Temp starts to go way up after about 5 minutes at 65mph. If I put it in neutral for 5 or 10 seconds and then drop back into drive the temp goes way down.

So it looks like the radiator is fine as well as the thermostat. All signs point to the water pump or some type of clog or crack in the water pump housing. (I would like to hold off on a cracked head diagnosis until the end).

It seems very strange though. The water pump is new! And looking at pictures it doesn't look physically possible that the vanes could be put on backwards. Maybe it's a pump from an older model that had a reversed coolant flow?

I don't have the old pump. I wish I had

pull it and take a picture. we'll compare it to ones we have.
could have gotten a gasser pump that spins the wrong way for your motor.

Ok, here's a picture of the water pump. Looks new and spins freely. There's a little surface corrosion because I've been using water to test with. Other than that it looks fine. I don't see how the impeller could have been put on wrong. Is this correct?

Attached Thumbnails

 

check your belt routing, just to be sure.

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2011 e320 cdi (132,000) current
2005 Jeep CRD diesel--2.8L (138,000 miles) wrecked, insurance took
1993 Mercedes benz 300D 2.5 Turbo Frybrid powered. (336,000 miles) wrecked and sold as parts car
1990 Mercedes benz 300D 2.5 Turbo (170,000 miles) wrecked and sold as parts car

Check out my Frybrid Vegtable Oil Conversion at http://1990300dfrybridconversion.shutterfly.com/

It's not about whether the impeller was installed correctly; it's about whether it's the correct impeller was installed.

That said, the impeller vane orientation does appear to be correct.

The belt routing was the first thing checked.

Well, if the vanes are oriented correctly and the pump is spinning, water should be flowing. But it's not. With the pump and housing off of the engine the next step will be to flush the block.

At what point should I stick a rag in the tank and light the car on fire?